Cysteinyl-tRNA Deacylation Can Be Uncoupled from Protein Synthesis

Aminoacyl-tRNA synthetases (ARSs) are critical components of protein translation, providing ribosomes with aminoacyl-tRNAs. In return, ribosomes release uncharged tRNAs as ARS substrates. Here, we show that tRNA deacylation can be uncoupled from protein synthesis in an amino acid specific manner. While tRNAs coupled to radiolabeled Met, Leu Lys, or Ser are stable in cells following translation inhibition with arsenite, radiolabeled Cys is released from tRNA at a high rate. We discuss possible translation independent functions for tRNACys

Two conformations of a crystalline human tRNA synthetase–tRNA complex: implications for protein synthesis

Aminoacylation of tRNA is the first step of protein synthesis. Here, we report the co-crystal structure of human tryptophanyl-tRNA synthetase and tRNA(Trp). This enzyme is reported to interact directly with elongation factor 1α, which carries charged tRNA to the ribosome. Crystals were generated from a 50/50% mixture of charged and uncharged tRNA(Trp). These crystals captured two conformations of the complex, which are nearly identical with respect to the protein and a bound tryptophan. They are distinguished by the way tRNA is bound. In one, uncharged tRNA is bound across the dimer, with anticodon and acceptor stem interacting with separate subunits. In this cross-dimer tRNA complex, the class I enzyme has a class II-like tRNA binding mode. This structure accounts for biochemical investigations of human TrpRS, including species-specific charging. In the other conformation, presumptive aminoacylated tRNA is bound only by the anticodon, the acceptor stem being free and having space to interact precisely with EF-1α, suggesting that the product of aminoacylation can be directly handed off to EF-1α for the next step of protein synthesis